This invention is directed to an additive/process aid for polymeric materials such as rubber elastomers. More particularly, this invention is directed to an additive/process aid for such polymeric materials to facilitate the processing and/or enhance the properties of the elastomers.
Polymeric materials such as rubber elastomers are used for the manufacture of various products including tire components such as tire tread, wedge compounds, sidewalls, bead filler and tire carcasses. However, it is well known that rubber elastomers tend to exhibit certain undesirable physical characteristics, such as, poor tear strength.
Tear strength or crescent tear is a measurement of the resistance of a material to tear forces. The higher the crescent tear measurement, the more difficult it is for the elastomer to be torn from whatever it is bonded to, such as steel.
Rubber elastomers also tend to exhibit weak tensile strength. Tensile strength is a measurement of the force at which a rubber elastomer can be expected to fail under a tension load. The tensile strength of the rubber elastomer is important in order to maintain its elasticity. Specifically, for rubber elastomers used in tires, the higher the tensile strength, then the more air pressure can be added to the tire, without fear of blowing the tire.
Finally, rubber elastomers tend to have a low elastic limit or tan delta measurement. The tan delta measurement is a measurement of the stress and strain exhibited on the elastomer or the amount of force that can be applied before the elastomer reaches its elastic limit and fails. It is advantageous for numerous applications to increase the elastic limit of rubber.
With particular regard to tire applications, it is desirable to produce rubber elastomers or elastomeric materials capable of exhibiting reduced hysteresis. Such rubber elastomers when fabricated into components for constructing articles such as tires, vibration isolators, power belts, and the like, will display properties of increased rebound, decreased rolling resistance and reduced heat-buildup when subjected to mechanical stress during normal use. Hysteresis refers to the difference between the energy applied to deform an article made from the elastomer and the energy released as the elastomer returns to its initial, un-deformed state. In pneumatic tires for instance, lowered hysteretic properties are associated with reduced rolling resistance and reduced heat build-up during operation of the tire. These properties, in-turn, result in lowered fuel consumption of vehicles using such tires and prolonged tire life. A reduction in the measured tan delta of the elastomer is indicative of a reduction in the hysteresis of the elastomer.
To address these undesirable physical characteristics, process aids and/or additives were introduced into the rubber elastomer composition. Process aids are substances added to aid in the production processing of the rubber elastomers. Additives are substances added to improve specific physical characteristics of the rubber elastomer. Additives can also act as process aids and aid in the processing of the elastomers.
Additives, such as calcium stearate and stearic acid, were used as process aids. However, the organic/organometallic nature of these substances causes them to have limited thermal stability and shelf life. Other prior process aids were products of organic chemical reactions. However, these process aids were not reproducible batch after batch and were often prone to error. Additives, such as carbon blacks and various silicas, were also added to improve, among other things, the tensile strength of rubber elastomers.
Thus, there is a need for a process aid which overcomes the limitations of the prior additives, and is a simple, low-cost product that improves the physical characteristics of rubber elastomers by providing increased tensile strength, elasticity and tear strength.
In accordance with the present invention, there is provided an additive/process aid for polymeric materials such as rubber elastomers or plastic materials which overcomes the limitations of earlier additives/process aids.
Further, in accordance with the present invention, there is provided an additive/process aid which provides a simple, quick, and low-cost, slow speed mixture blend which produces a stable product. It also improves the physical characteristics of rubber elastomers, by providing, among other things, increased tensile strength, elasticity, and tear strength.
The additive/process aid comprises a mixture of comminuted or micronized shale/slate predominately formed of aluminum, magnesium and/or iron silicates, starch, a reactive resin component, a metal carbonate and an acidic component such as a fatty acid or a silica gel.
As used herein, comminuted shale/slate includes gray slate flour (alumina silicate or ground shale) as well as silicates of aluminum, magnesium and iron and mixtures thereof. The gray slate flour is typically in powder form to assist in its dispersion in the polymeric material.
Starch may be obtained from most agricultural crops; the dominant starch raw materials being potato, cassava, corn and wheat. Corn starch is preferred and the present invention is described with particular reference to the use of the same.
The resin component is selected from the group of reactive polyesters resins and epoxy resins. The reactive cite of the polyester resin may comprise a carbon-carbon unsaturation intermediate ester groups. Preferred polyesters include those used in structural applications such as reinforced laminates. The epoxy resin may comprise a wide range of epoxies as described below, but epoxidized soybean oil is preferred.
The metal carbonate preferably includes a metal selected from Group IA or IIA of the Periodic Table. Calcium carbonate is preferred and described below.
The acidic component may comprise silica gel or a fatty acid. Useful fatty acids include stearic acid and oleic acid.
The additive may be formulated with reduced amounts of metal carbonate and increased amounts of the remaining ingredients varying up to about: 30% flour, 35% starch, 15% resin, 5% metal carbonate and 15% acidic component, by weight, wherein the aggregate amount of the ingredients total 100%. On the other hand, the metal carbonate may be increased and the remaining ingredients reduced to about: 10% flour, 10% starch, 5% resin, 70% metal carbonate and 5% acidic component, by weight, wherein the aggregate amount of the ingredients total 100%. Additive/process aids having these xe2x80x9chighxe2x80x9d and xe2x80x9clowxe2x80x9d formulations have provided improvements with acceptable trade-offs in certain of the composition properties readily identified by the skilled compounder.
In preferred compositions, the additive/processing aid comprises from 10 to 30% shale/slate material, 10 to 35% starch, 5 to 15% resin, 10 to 40% metal carbonate, 5 to 15% acidic component, by weight, wherein the aggregate amount of the ingredients total 100%. More preferably, the additive/processing aid comprises from 20 to 30% shale/slate, 20 to 35% starch, 5 to 10% resin, 20 to 35% metal carbonate, 8 to 15% acidic component, by weight, wherein the aggregate amount of the ingredients total 100%.
Preferred additive/processing aid compositions including polyester resin and silica gel comprise from 20 to 29% gray slate flour, 18 to 28% corn starch, 4 to 8% liquid polyester, 10 to 20% calcium carbonate, 8 to 15% silica gel, by weight, wherein the aggregate amount of the ingredients total 100%. More preferably, the additive/processing aid contains about 29% gray slate flour, about 28% corn starch, about 8% liquid polyester, about 20% calcium carbonate, about 15% silica gel, by weight, wherein the aggregate amount of the ingredients total 100%.
Preferred additive/processing aid compositions including epoxy resin and a fatty acid comprise from 20 to 30% gray slate flour, 20 to 35% corn starch, 5 to 10% epoxy, 10 to 20% calcium carbonate, 10 to 15% fatty acid, by weight, wherein the aggregate amount of the ingredients total 100%. More preferably, the additive/processing aid contains about 25% gray slate flour, about 25% corn starch, about 5% epoxy resin, about 35% calcium carbonate, about 10% fatty acid, by weight, wherein the aggregate amount of the ingredients total 100%.
As noted above, the resin may comprise a polyester resin or an epoxy resin. The resins are preferably liquid at rubber processing conditions and have a molecular weight of from about 200 up to about 10,000 or higher.
Suitable epoxy compounds comprise molecules having at least one or more epoxide group per molecule and include epoxidized alkanes, alkenes, cycloalkanes, alkenes an other epoxidized polymers and chemicals. For example, epoxy/ether, epoxy/hydroxyl, epoxy/ester, epoxy/amine ether/amine, and cycloaliphatic ether/hydroxyl group. These compounds contain aliphatic and/or cycloaliphatic groups. Examples include Octyl Epoxy Tallate (Argus Chemical and Union Carbide), Epoxyprene 25 and 50 (Epoxidized Natural Rubber from Guthrie Latex), Epon (Epoxidized Bispheno A from Shell Oil Co.), Styrene Oxide (S500-6 Aldrich Chemical Co.) and 1,2-Epoxy-3-phenoxypropane (24,848-7 Aldrich Chemical Co.). Epoxidized plant (or vegetable) oils, such as epoxidized soybean oil(copyright) C P Hall PARAPLEX G62, Argus Chemical, Union Carbide and Harwick Standard) and epoxidized linseed oil (Argus Chemical), are most preferred.
The additive/processing aid is preferably added to polymeric materials such as rubber elastomers or plastic materials such as polyethylene, ethylene propylene. The preferred rubber elastomers are selected from the group consisting of natural rubber, isoprene, chloroprene, halo-butyls, SBR rubber, butyl rubber, neoprene, epichlorohydrin rubber, polysulfonated rubber, silicone rubber and mixtures thereof.
These and other aspects of the invention are described below in further detail, the illustrated embodiments being representative of only some of the ways in which the principles and concepts on the invention can be executed and employed.